For example, in a process of manufacturing a semiconductor device, various kinds of heat treatment apparatuses have been used in order to perform chemical vapor deposition (CVD), diffusion, oxidation, annealing or the like on a target object of a semiconductor wafer. Above all, in a CVD treatment and a diffusion treatment under a depressurization with a relative high pressure, the heat treatment apparatus has a vertically extending reaction tube which is made of quartz and supported by a manifold made of metal, which has a gas introduction unit and an exhaust unit. A processing region within the reaction tube accommodates the semiconductor wafers therein, which are held in a multistage manner by a holding unit such as a wafer boat. After the processing region sealed, it is heated to a predetermined process temperature by a heater installed outside the reaction tube. As such, a predetermined heat treatment is performed with respect to the semiconductor wafers with a predetermined process gas under a predetermined process pressure.
In such a heat treatment apparatus, the reaction tube has a double tube structure including an inner tube and an outer tube, which are made of quartz. The inner tube is supported by a support ring formed on an inner surface of the manifold. A concave portion is formed at a lower end outer periphery of the inner tube. A protrusion, which engages the concave portion to position a circumferential direction of the inner tube, is formed in the support ring.
The support ring thermally expands or contracts during the process of the heat treatment as a temperature within the reaction tube changes. When the support ring thermally expands or contracts, the inner tube may be dislocated on the support ring.
At this time, the concave portion of the inner tube may thermally contract in a state where it is in contact with the protrusion of the support ring and the inner tube may be interposed between a contact point, at which the concave portion is in contact with the protrusion, and an opposite position to the contact point. As a result, a vicinity of the concave portion having a weak strength may be broken.